Last night I decided to pull the spark plug out of one of my Eigers to see how it was running. The plug looked good, but I noticed the plug threads into the head so that the threads are actually exposed inside the combustion chamber.... like atleast 1/8" of the threads were black. Is this normal or should I look into getting shorter plug with less threads? I worry that after a while, carbon will build up on the threads and then I'll destroy the threads in the head removing it.

 

The carbon should never build up to the extent that you'll junk the threads on the head. Well maybe if the plug has been in the bike w/ the bike sitting for a VERY LOOONG time, but it's still unlikely. If you get a shorter plug the electrode will be farther away from the combustion center so it could possibly affect your running/tuning detrimentally. Just stick w/ the style of plug in the bike, as long as you keep up on the maintenance and not do things like use alot of force tightening the spark plug, putting the plug in the motor while it's still hot, or never doing your periodic maintenance you should never have a problem.

 

Id use whatever plug is called out in the owners manual. Sometimes theres a large champher on the bottom of the threads, and this is a place for soot and carbon to go, but it shouldnt cause any problems. If you use a dab of anti seize on the spark plug threads, you shouldnt have to worry about it coming out next time.

 

Thanks for the comments guys. I'll just pull them a few times a year and check 'em out.

 

What color should the plug tip be if mix is RIGHT?

 

Here's a good site:

http://www.maxracesoftware.com/spark_plugs.htm

 

Heres another site
reading plugs
And as it was writen in the articles


Mostly valid only for full-load dyno tests ,
or if engine is quickly turned-off after
finish line, and then towed back to pits,
and spark plugs removed for readings there !

If you dont do the plug chop correctly, the readings are meaningless.

 

Thanks guys,,,,,interesting article! Was pertaining to drags but helpful.

I guess the best way to test ATV is rev her up and shut off immediately,,,,look for dark gray or tan in upper portion of cone

 

Not quite. Revving in neutral wont do a thing...the engine needs to be under load for an accurate chop.
Heres an article, and it describes how to do a plug chop reading.
plug chop how to

 

Thanks again,,,,,good article